Light-emitting diodes (LEDs), also known as luminescent diodes, are optoelectronic components which when in operation emit electromagnetic radiation with wavelengths in the ultraviolet, infrared or indeed in the part of the electromagnetic spectrum perceptible to the human eye.
Furthermore, they have numerous potential uses. For example, typical high power light-emitting diodes already produce a light intensity of several watts and are thus suitable and usable as headlights and for projection lighting. On the other hand, LEDs are used as status indicators, luminescent devices of the most varied wavelengths, warning lamps, for data transmission, in display elements and for many other purposes.
To produce the electromagnetic radiation, light-emitting diodes in special semiconductor lattice structures in particular make use of the energy gap between the conduction band and the valence band. The difference between the energy levels of the valence band and the conduction band is here understood as a band gap, wherein, in the case of semiconductor materials with direct band transition, the highest energy state in the valence band lies directly below the lowest energy state of the conduction band. Through energy input, electrons change from the lower energy state of the valence band to the higher energy state of the conduction band. On recombination of these electrons into the valence band the electrons release this introduced energy in the form of electromagnetic radiation of a specific wavelength.
By introducing a luminescence conversion element into the beam path of the emitting semiconductor, it is possible to convert the primarily produced wavelength into a secondary wavelength. It is thus simply possible to generate mixed light, for example white light or light of a particular wavelength which does not correspond to the band gap of the semiconductor in question.
A light-emitting diode may be mounted in different ways. On the one hand LEDs may be mounted on a printed circuit board using surface mount technology (SMT). This space-saving variant saves on additional contact pins in the case of special shapes, since the electrical terminal may be fitted to an outer side of the housing in the form of a pad or an electrically conductive plate and comprises an electrical connection to the semiconductor chip inside the housing.
A further variant for mounting light-emitting diodes involves providing the LED housing with contact pins for mounting on a perforated printed circuit board. For this purpose, the terminals provided for electrical operation must be specially configured. In this case, a light-emitting diode chip is introduced into a housing, preferably a casting compound which is partially transparent to the emitting wavelength.
Electrical connection of the emitting chip is then effected by way of additional discrete contact pins extending out of the housing.
For those instances in which light-emitting diodes are not mounted directly on printed circuit boards, since they may possibly be used relatively far away therefrom, such as for example in appliance fronts, or in a primitive application in which a printed circuit board design would not be convenient, there are LED auxiliary elements, for example socket adapters, which electrically and/or mechanically connect a conventional LED by means of plug-and-socket systems and/or holders.
In order to increase luminance for an application, a plurality of light-emitting diodes are for example placed and mounted together on a printed circuit board. In the field of projection technology, backlighting is for example produced for liquid crystal screens, or liquid crystal displays (LCD), by means of a white light LED matrix, a matrix of a plurality of white light LEDs serving as backlighting.
A disadvantage of all these methods is that additional elements, such as terminal elements in general or adapters, are required to operate a light-emitting diode. Added to this is the disadvantage that an LED which has been manufactured for a particular type of mounting can only be used to a limited extent for further mounting methods. Finally, an assembly of LEDs can likewise only be produced using additional elements. This means that losses arise due to additional evolution of heat and a greater space requirement.